Design and engineering practice of HVDC SSDC for suppressing sub-synchronous oscillations

The inter-transmission of sub-synchronous electrical parameters between AC and DC sides of HVDC power transmission system is analyzed by switching functions of converter, and in term of sub-synchronous frequency the mechanism of sub-synchronous oscillations (SSO) in power grid caused by the control system of HVDC system is expounded. By use of complex torque coefficients in time-domain simulation the sub-synchronous damping characteristic of AC/DC power grid is researched in detail, and the principle of suppression SSO by supplementary sub-synchronous damping controller (SSDC) is emphatically discussed, then the design approach for the design of modal control-based SSDC is proposed. In allusion to an actual SSO occurred in a certain power grid in China, a modal control-based SSDC is designed. The correctness of the principle applied in the design of modal control-based SSDC and its effectiveness in suppressing SSO are verified by time-domain simulation.